1. Field of the Invention
The present invention relates to a plastisol composition that forms coatings or molded articles having excellent anticreep property. More specifically, the invention relates to a plastisol composition of an acrylic resin which maintains excellent fluidity required for the coating and molding even after preserved for extended periods of time and further exhibits excellent gelation property upon heating, enabling the obtained coating or the molded article to exhibit excellent resistance against the relaxation of stress.
2. Description of the Prior Art
Plastisol compositions have been widely used for forming gaskets and liners for hermetically sealing container closures and the like for the reasons that they have excellent fluidity, they do not contain volatile components such as solvents, they are gelled upon heating to form molded articles of any shapes and that they have suitable degrees of softness and cushioning property.
The plastisol is obtained by using a liquid plasticizer as a dispersing agent and dispersing therein resin grains of emulsion sizes or suspension sizes. Though the dispersed state is maintained at room temperature, the resin grains absorb the plasticizer at high temperatures and are merged and are plasticized. Homopolymers and copolymers of a vinyl chloride have heretofore been widely used as resins emitting, however, hydrogen chloride into the open air and further emitting harmful substances such as dioxines when they are incinerated. Therefore, there has already been proposed to use a plastisol of an acrylic resin.
For instance, Japanese Patent Publication No. 26263/1981 discloses a thermally merging acrylic resin plastisol which contains grains of a single-phase acrylic polymer or copolymer containing at least 60% by weight of alkyl acrylate or methacrylate units but without containing a surfactant, said polymer or said copolymer being non-volatile at room temperature and is dispersed in a medium that has the same chemical structure as the monomer of said polymer or said copolymer but that does not contain the surfactant, and said polymer or said copolymer containing a compatible liquid plasticizer which is not a monomer.
There has further been known a reactive plastisol of a non-vinyl chloride resin. For instance, Japanese Patent Publication No. 12772/1989 discloses a reactive plastisol which is insoluble in a plasticizer at room temperature and is plasticized at high temperatures, comprising a polyvinyl acetal resin, an epoxy resin, or a combination thereof with a polyester plasticizer, and a curing agent of an epoxy resin.
Furthermore, Japanese Laid-Open Patent Publication No. 161849/1987 discloses a reactive plastisol comprising a polyether or a polyester plasticizer modified with a polymethacrylate resin or an isocyanate, and a thermal reaction starter and an optical reaction starter.
However, the known acrylic plastisol proposed above has pot life which is inferior to that of a plastisol composition of a vinyl chloride resin, loses fluidity while it is being preserved, and fails to exhibit gelation property to a sufficient degree after preserved. Moreover, the coating or the molded product obtained by gelling the acrylic plastisol upon heating exhibits insufficient anticreep property particularly when it is heated.
The containers and container closures are provided with a gasket or a lining composed of a plastisol to accomplish the sealing. However, the gaskets and linings composed of the acrylic resin plastisol exhibit anticreep property that is very inferior to that of the gaskets or linings composed of a vinyl chloride resin plastisol, and develop such troubles as creeping and breakage due to the heat at the time of hot-filling and retort-sterilization, permitting the content to leak.